1. Field of the Invention
The present invention relates to a passive coherent location (xe2x80x9cPCLxe2x80x9d) radar system and method, and more particularly, to a system and method for associating a line track with a target and tracking the target in PCL radar applications.
2. Discussion of the Related Art
PCL radar systems may be represented by a multistatic radar system. A multistatic radar system has a number of receivers that are separated from one or more transmitters. The radiated signal from a transmitter arrives at a receiver via several separate paths. One path may be a direct path from the transmitter to the receiver, and the other path may be a target path that includes an indirect path from the transmitter to a target to the receiver. Measurements may include a total path length, or transit time, of the target path signal, the angle of arrival of the target path signal, and the frequency of the direct and target path signals. A difference in frequency may be detected if the target is in motion according to a doppler effect.
Knowledge of the transmitted signal is desirable at the receiver if information is to be extracted from the target path signal. The transmitted frequency is desired to determine the doppler frequency shift. A time or phase reference also is desired if the total scattered path length is to be determined. The frequency reference may be obtained from the direct signal. The time reference also may be obtained from the direct signal provided the distance between the transmitter and the receiver is known.
Multistatic radar systems may be capable of determining the presence of a target within the coverage of the radar, the location of the target position, and a velocity component, or doppler, relative to the radar. The process of locating the target position may include a measurement of a distance and the angle of arrival. The measurement of distance relative to the receiving site may include both the angle of arrival at the receiving site and the distance between transmitter and receiver. If the direct signal is available, it may be used as a reference signal to extract the doppler frequency shift.
In PCL radar systems, transmitters may be known as illuminators. Illuminators may be wideband sources of opportunities that include commercial frequency modulated (xe2x80x9cFMxe2x80x9d) broadcast transmitters and/or repeaters, commercial high-definition television (xe2x80x9cHDTVxe2x80x9d) broadcast transmitters and/or repeaters, and the like. Techniques for wideband signal pre-detection processing and co-channel interference mitigation exist. Approaches may include an array of antennas used to receive the source of opportunity to be exploited, such as the primary illuminator, and any other co-channel signals present in the environment.
PCL systems may receive a multitude of direct and reflected signals from several different transmitters. The signals should be identified and associated with the appropriate target. Further, several targets may be scattering signals in different locations. The different signals and their measurement data should be associated with the appropriate target. If the target does not exist, then a new tracking may have to be implemented for the target. Conversely, old trackings should be eliminated from the system if updates are no longer being received. More efficient and expedient measurement data association may improve target tracking in PCL systems.
Accordingly, the present invention is directed to PCL applications and signal processing. Thus, a system and method for central association and tracking within PCL applications is disclosed herein.
According to an embodiment, a method for associating a line track with a target for a passive coherent location system is disclosed. The method includes receiving a detection report having the line track that corresponds to the target. The method also includes computing a target state and state covariance for measurements of the line track. The method also includes scoring the line track according to the target state and the state covariance. The method also includes assigning the line track to a target track according to the scoring.
According to another embodiment, a method for associating and tracking target data within a passive coherent location system is disclosed. The target data includes measurements. The method includes computing a target state and state covariance from the measurements. The method also includes assigning a line track correlating to the target data to a target track according to the target state and the state covariance. The method also includes initializing the target track. The method also includes initializing a filter according to the target state and the state covariance. The method also includes tracking the target track with the filter. The method also includes extrapolating the target data from the target track.
According to another embodiment, a method for associating a line track to a target track from target tracking operations within a passive coherent location system is disclosed. The method also includes determining a candidate association combination for the line track. The method also includes applying at least one gate to the candidate association combination. The method also includes estimating a target state and a state covariance for the line track. The method also includes computing a score for the candidate association combination according to the target state and the state covariance. The method also includes assigning the line track to a target track according to the score.
According to another embodiment, a method for filtering a target track correlating with a detection report having measurements associated with a target within a passive coherent location system is disclosed. The method includes computing corrections for a target state and state covariance for the detection report. The method also includes updating the target state and state covariance with the corrections. The method also includes propagating the target track with the updated target state and the updated state covariance.
According to another embodiment, a system for estimating target parameters for a target is disclosed. The system includes detection reports comprising measurements. The system also includes a line track association function to associate a line track correlating to the detection reports to a target track. The system also includes a track filtering function to propagate the target track according to the measurements. The system also includes a target extrapolation function to calculate the target parameters from the target track and the measurements.
According to another embodiment, a system for associating a line track to a target track is disclosed. The line track correlates to at least one detection report. The system includes a nonlinear least squares batch estimator to compute a target state and state covariance for measurements from the at least one detection report and to score a candidate associate combination for the line track. The system also include a line track assignment function to assign the line track according to the score for the candidate associate combination.
According to another embodiment, a system for track filtering a target track is disclosed. The target track is associated with a line track from at least one detection report. The system includes a filter to compute corrections to a target state and state covariance to update the target track using a means for computing measurement residuals and partial derivatives of measurements from the detection report. The system also includes a validity check function to check the updated target track using a velocity magnitude component and an acceleration magnitude component.
Additional features and advantages of the invention will be set forth in the disclosure that follows, and in part will be apparent from the disclosure, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.